Visual document navigation and querying systems

A number of visualization systems have attempted to facilitate document navigation by

displaying the entire document on screen.

The first of these is the Document Lens (Mackinlay & Robertson 1993) (see Figure 10), which allows the entire document to be viewed at once, fully displaying the page of

interest while keeping the rest of the document viewable, if not readable. Keyword searches can be performed and the results are displayed by highlighting the word

wherever it appears in the document. The mode of overview here is primarily visual as opposed to semantic, since text outside the focus region is very hard to read. It is

unclear whether this kind of overview is very helpful and there has been no published

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Figure 10 The Document Lens (Mackinlay & Robertson 1993)

Figure 11 Text in 3D (Small 1999)

Small experim ented with alternative ways o f laying text out in three dim ensions (Sm all 1999). The plays of Shakespeare w ere laid out so that the structure o f the play could be seen all at once (see Figure 11). This kind of design only m akes use o f the third dim ension as a m etaphor to support zoom ing. The feature m ost useful for goal directed reading, the highlighting o f portions o f text relevant to queries, can easily be handled with a 2D overview o f the text (see 3.4.1). Also, any advantages available for goal-directed reading w ould need to outw eigh the difficulties introduced by the use o f 3D, such as the difficulty o f navigating in 3D space and o f reading text that is not parallel to the view plane (Small 1999).

A nother 3D visualisation o f single docum ents is the 3D book (Card, R obertson & York 1996; W oodruff et al. 2000). Here an entire book or a collection o f web pages is represented using a 3D book m etaphor. The user is able to turn to specific pages, turn

Chapter 2 section 3 69

pages one at a time, or rifle through the pages seeing w hat is on each page as it turns. This visualization offers very fam iliar navigation and a good m etaphor for presenting collections of inform ation. N evertheless, it does not directly attem pt to support goal- directed search, and it is not clear that it w ould be able to do so.

Turning to 2D interfaces, H om bæ k and F rpkjæ r applied tw o standard visualisation techniques to the support o f reading and evaluated their effectiveness (H om bæ k &

F rpkjæ r 2001). They com pared a standard lin ear docum ent brow ser to a

overview +detail interface and a fisheye interface. The three interfaces used in the evaluation are shown in Figure 12. In the fisheye interface, traditionally m ore inform ative portions o f the docum ent (such as the first and last paragraphs) are at a readable size, the rest are m uch reduced - the user can expand these by clicking on them . The overview +detail view is m uch like those described in 3.4.1, except that headings are m aintained at a readable size.

a) Linear b) Fisheye c) O verview +D etail

Figure 12 Three docum ent visualisations (Hornbcek & Fr0kjcer 2001)

Tw o tasks w ere evaluated, one was characterised as ‘re ading-to-leam -to-do’, and the oth er was a goal-directed reading task. In the ‘reading-to-leam -to-do’ task, the

interfaces were used to read a document. Performance was judged by measuring reading

times, and scoring subsequently written précis and answers to unanticipated questions.

In the goal-directed type of reading, performance was measured by giving the

participants six questions, one at a time, recording task times and marking their answers.

The results of this analysis favoured the overview-kdetail interface. It produced

significantly higher subjective satisfaction scores. It also delivered significantly better

answers for the ‘reading-to-leam-to-do’ task, although not for the goal-directed one.

However, the overview-t-detail interface resulted in significantly slower performance in

both tasks. The fisheye interface resulted in worse question answering and subjective satisfaction scores than the linear and overview-i-detail interfaces, although it was faster

for the ‘reading-to-leam-to-do’ tasks. This evaluation suggests that the overview-hdetail interface visualisations allow for a better understanding of the document, although they

can slow performance.

A number of design guidelines can also be distilled from the work reviewed in this

section. Although several interfaces have used 3D, it is not clear that these would offer particular advantages for goal-directed search; additionally, no evaluations have been

published to suggest otherwise. Therefore, given the additional complexity introduced

by the use of 3D, 2D interfaces are currently preferable. Tuming to 2D interfaces, an

evaluation is described which shows the relative advantages, for supporting goal-

directed reading, of two visualisation techniques, overview4-detail and fisheye. This evaluation suggests that an overview4-detail interface with a document thumbnail as an

overview can improve understanding at the cost of slowing performance.